Japanese Patent Application Laid-Open No. S63-205460 (Patent Document 1) describes that, in an internal combustion engine which includes plural cylinders each provided with one spark plug for an ignition thereof, an ignition control signal (ignition signal) is output at different timing for each spark plug of the cylinder so that the ignition control signals of the respective spark plugs of the cylinders do not overlap with each other.
Japanese Patent Application Laid-Open No. H08-128381 (Patent Document 2) discloses an ignition apparatus for an internal combustion engine, wherein the ignition apparatus outputs an ignition signal from an ECU to an igniter, and detects an ignition state based on a fail signal returned from the igniter. In the above ignition apparatus, a single signal line is employed as both a signal line for the ignition signal and a signal line for the fail signal; and when the fail signal overlaps with the ignition signal, the level of the fail signal is lowered relative to the level of the ignition signal.
Patent Document 1: Japanese Patent Application Laid-Open No. S63-205460
Patent Document 2: Japanese Patent Application Laid-Open No. H08-128381